Electric grab



Oct. 7, 1969 J. A. MARTIN ET 3,471,194

ELECTRIC GRAB Filed Dec. 26, 1967 2 Sheets-Sheet 1 Oct. 7, 1969 J. A.MARTIN ETAI- 3,

ELECTRIC GRAB Filed Dec. 26, 1967 2 Sheets-Sheet 9 United States3,471,194 Patented Oct. 7, 1969 3,471,194 ELECTRIC GRAB Jean AntoineMartin, Bagneux, Pierre Mauguen, Montfermeil, and Jacques Pinault,Paris, France, assignors to Groupement Atomique Alsacienne Atlantique,Le

Plessis-Robinson, France Filed Dec. 26, 1967, Ser. No. 693,344 Claimspriority, applicatignlltrance, Dec. 29, 1966,

Int. Cl. I566c 1/06 US. Cl. 294-88 4 Claims ABSTRACT OF THE DISCLOSUREThis invention relates to an electric grab and is more specificallyconcerned with the means which are associated with the handling tongs orgrab jaws in order to carry out the controlled locking of said jaws andto ensure operational safety and reliability of the grab.

It is already a known practice to make use of electric grabs of the typecomprising a body on which an electromagnet is supported axially, twoholding jaws which are freely mounted inside said body on each side ofthe electromagnet and each rigidly fixed to a member formed ofnon-magnetic material and a slightly curved flexible strip which servesto interconnect the two jaws so that said jaws are attractedsimultaneously as and when the electromagnet is energized and are thuscaused to pivot laterally by deformation of the flexible strip.

Moreover, arrangements which have already been contemplated in a grab ofthis type consist in mounting a locking device which makes it possibleto lock the jaws in their rest position in order to prevent anyunexpected movement of these latter during the different operationsinvolving transfer of an object which is being carried by said jaws. Forthis purpose, a grab of this type comprises a second electromagnet and amagnetic pallet supported by the extremity of a leaf spring which isrigidly fixed at the extremity thereof so that, when no voltage isapplied to the electromagnet, said pallet serves to maintain the jaws inoutwardly displaced relation by engagement of these latter within arecess formed between two shouldered portions respectively formed oneach jaw. When the second electromagnet is energized, the pallet iswithdrawn from its recess and the grab jaws are consequently released.

However, it is essential to ensure that a grab of this type shouldafford full reliability of operation without any danger of accidentalopening or closure of its jaws during handling operations. In point offact, operational reliability may not be fully ensured by means of thelocking system of the type considered above, in particular when axialshocks occur and tend to dislodge the locking pallet from its recess.

In fact, in order that a pallet having a weight M which is subjected toa restoring force F by its spring and which has an unlocking travel Cshould not be accidentally released under the action of an impact whilstthe grab is endowed with a velocity V, the relation:

must be satisfied. However, this inequality cannot be satisfied in allcases, 1n particular at high velocities. In fact, the force developed bythe electromagnet must be greater than the force F in order to initiatea grab release and this is not always possible, especially for reasonsof permissible size of said electromagnet.

The aim of the present invention is to circumvent the above-noteddisadvantage and is more especially concerned with an improved lockingdevice whose operation is no longer dependent on the relation statedabove, said device being characterized in that it comprises jaw-lockingmeans which are insensitive to axial accelerations of said grab, saidmeans being maintained in the locking position by a spring-loaded memberwhose action is exerted in a plane at right angles to the longitudinalaxis of the grab and being brought into the unlocking position by meansof an electromagnet which produces a set of forces in opposition to theaction of said member.

In a first alternative embodiment, said locking means comprise a palletformed of magnetic material and rotatably mounted between the armaturesof the electromagnet, said pallet being rigidly fixed to a shaft locatedat right angles to its plane and coupled to a second pallet havingdimensions such that the extremities thereof are engageable in thejaw-locking position within a circular recess formed in a shoulder whichis provided on each grab jaw, and a spring mounted in coaxial relationwith said shaft so as to work under torsional stress and to maintainsaid second pallet in the locking posi ion, the unlocking of said jawsbeing obtained by energizing said clectromagnet which produces thelimited rotational motion of said pallets in opposition to the action ofsaid spring.

The movement of rotation of the shaft which interconnects said palletscan be carried out on roller-bearings, on plain bearings, by means offlexible articulations, knife-edge articulations and so forth.

In another alternative embodiment, said locking means comprise at leasttwo arms which are symmetrical with respect to the center-line of saidgrab and pivotally mounted in their plane about pivot-pins which arecarried by said grab, a spring which is adapted to initiate in thelocking position a radial displacement of said arms towards theperiphery of said grab, and an electromagnet which is adapted to effectthe unlocking of the grab jaws by attracting said arms in the oppositedirection in opposition to the action of said spring.

The different features of the invention will now be explained in detailin the following description of two exemplified embodiments which aregiven solely by way of indication and not in any limiting sense,reference being had to the accompanying drawings, in which:

FIG. 1 is a vertical sectional View taken along line 1-1 of FIG. 2 andshowing a locking device comprising a rotary pallet in a first form ofexecution;

FIGS. 2 and 3 are horizontal sectional views taken respectively alonglines 11-11 and HI-IH of FIG. 1;

FIG. 4 is a vertical sectional view taken along line IV-IV of FIG. 6 andshowing a second alternative embodiment of the locking device;

FIG. 5 is a vertical sectional view taken along line V-V of FIG. 6;

FIG. 6 is a horizontal sectional view taken along line VI-VI of FIG. 4.

In FIG. 1, the grab which is illustrated comprises a body 1 ofsubstantially cylindrical shape inside which is fixed axially anelectromagnet 2 composed of a former 3 and coil 4. The former 3 is madeup of two identical parts of mild steel separated from each other by anonmagnetic plate 5. A second electromagnet 7 is attached to saidelectromagnet 2, a non-magnetic partition plate 6 being advantageouslyprovided between said electromagnets in order to isolate theirrespective circuits. The electromagnet 7 also comprises a core 8 and acoil 9.

The two grappling tongs or grab jaws which are designated respectivelyby the reference numerals 10 and 11 are mounted within the body 1 oneach side of the electromagnet 2. Each jaw is provided at the lower endthereof with a nose 10a or 11a, thereby enabling the grab to grip anyobject (not shown in the drawings) by engagement of its two noses in acircular channel formed in said object. The jaws 10 and 11 are providedrespectively at the upper ends thereof with extensions in the form oftwo members 12 and 13 which are made of nonmagnetic material and whichare applied against the top face of the electromagnet 2. These twomembers 12 and 13 are interconnected by means of a metallic strip 14which is secured at each extremity. Said strip has a very slightlycurved profile which makes it possible to exert an upwardly directedforce on each of its extremities and, in fact, on the members 12 and 13to which said extremities are rigidly fixed, thereby producing a lateralmovement of separation of the jaws when the electromagnet 2 is notenergized. In the central portion thereof, the strip 14 is maintainedapplied against a block 16 which is rigidly fixed to the top face of theelectromagnet 2 by means of a fixing screw 17 having an extended lengthwhich penetrates into the partition plate 5.

In this grab, which is of a type already known per se, it is theelectromagnet 2 which controls the movement of separation or of closureof the jaws in combination with the fiexible strip 14. However, byreason of the very flexibility of said strip, it is apparent that thejaws must be instantaneously arrested or locked in position in order toprevent any maloperation or accidental detachment of loads, especiallywhen the grab is liable to be subjected to shocks or accelerations.

For the purpose aforesaid and in the form of execution which isillustrated in FIGS. 1, 2 and 3, the coil unit 9 of the electromagnet 7is placed around the central core 8 and surrounded by a hollow cylinder50 which is screwed onto said core. Said cylinder 50 is provided at thelower end with two abutment shoulders 51 and 52, the profile of which isshown in the sectional view of FIG. 2. Between the cylinder 50 and thelower end of the central core 8, there is fitted a first pallet 53, theplane of which is located at right angles to the center-line of thegrab 1. Said pallet is rigidly fixed at its center to a shaft 54 carriedby a stationary bearing support 55 in which said shaft is capable ofrotating freely on ball bearings 56 or the like. The shaft 54 is rigidlyfixed at the lower end thereof to a second pallet 57 which is parallelto the first and has slightly larger diametrical dimensions. Theextremities 58 and 59 of said second pallet are capable of engaging insuitable shoulders formed on the corresponding faces of the jaws 10 and11. A helical spring 60 is mounted around the shaft 54, said springbeing secured at one end to the stationary bearing support 55 and at theother end to the second pallet 57, with the result that said springcontinuously tends to place said pallet in the position shown in FIG. 3in which its extremities 58 and 59 lock the jaws 10 and 11 in position.Under these conditions, the device herein described locks said jaws andmaintains these latter in the open position. In this position, as shownin FIG. 2, the first pallet 53 is in turn placed in such a manner thatthe extremities thereof cooperate with the abutment shoulders 51 and 52of the hollow cylinder 50.

In order to carry out the unlocking operation, the electromagnet 7 isenergized; the electromagnetic driving torque thus produced causes thepallet 53 to pivot about its axis until it is brought into contact witha stop 61 carried by the grab body. The second pallet 57 follows thepallet 53 in its rotational motion and its extremities 58 and 59 arefreed from the corresponding shoulders, thereby freeing the grab jaws 10and 11 which can then be caused to close by energizing the mainelectromagnet 2 of the grab.

Referring now to the form of execution which is illustrated in FIGS. 4to 6, it can be seen that the locking device essentially comprises twoarms 70 and 71 disposed symmetrically with respect to the center-line ofthe grab in a plane substantially parallel to that of each of the jaws10 and 11. Said arms 70 and 71 are pivoted respectively on the grab bodyabout pins 72 and 73 and are associated with two small plates 74 and 75of magnetic material which are mounted opposite to the poles of thelocking electromagnet 7. As in the embodiment of FIGS. 1 to 3, saidelectromagnet comprises a central core 8 and a coil 9. The lowerportions of the arms 70 and 71 are curved and joined together by meansof a spring 76 which continuously urges the arms outwards by causingthem to pivot in their plane. In this position, the arms 70 and 71 areadapted to cooperate with two segments 77 and 78 of generally circularshape which are rigidly fixed to the jaws 10 and 11 in such a mannerthat the central portion of said arms comes into engagement between saidsegments, thereby maintaining the jaws in their open position, theoutward displacement of the arms being limited by stops 79 which arecarried by these latter and which come up against the correspondingedges of the segments. When the electromagnet 7 is energized, the smallmagnetic plates 74 and 75 are attracted by the electromagnet andinitiate the pivotal motion of the arms about their pivot-pins 72 and 73in opposition to the action of the spring 76. Said arms then move awayfrom the segments 77 and 78 and towards each other, thereby permittingoperation of the jaws by means of the main electromagnet 2.

As is readily understood, the invention is not limited solely to theexamples herein described and illustrated but extends, on the contraryto all alternative forms. In particular, the two forms of constructionwhich have been more specifically described could be employed incombination in order to endow the grab with even greater safety andreliability despite any mechanical stresses to which it may besubjected.

What is claimed is:

1. An electric grab fitted with two jaws which are controlled both foropening and closure, wherein said grab comprises jaw-locking means whichare insensitive to axial accelerations of said grab, said means beingmaintained in the locking position by a spring-loaded member whoseaction is exerted in a plane at right angles to the longitundinal axisof the grab and being brought into the unlocking position by means of anelectromagnet which produces a set for forces in opposition to theaction of said member.

2. An electric grab as claimed in claim 1, wherein said locking meanscomprise a pallet formed of magnetic material and rotatably mountedbetween the armatures of the electromagnet, said pallet being rigidlyfixed to a shaft located at right angles to its plane and coupled to asecond pallet having dimensions such that the extremities thereof areengageable in the jaw-locking position within a circular recess formedin a shoulder which is provided on each grab jaw, and a spring mountedin coaxial relation with said shaft so as to work under torsional stressand to maintain said second pallet in the locking position, theunlocking of said jaws being obtained by energizing said electromagnetwhich produces the limited rotational motion of said pallets inopposition to the action of said spring.

3. An electric grab as claimed in claim 1, wherein said locking meanscomprise at least two arms which are symmetrical with respect to thecenter-line of said grab and pivotally mounted in their plane onpivot-pins which are carried by said grab, a spring which is adapted toinitiate in the locking position a radial displacement of said armstowards the periphery of said grab, and an electromagnet which isadapted to elfect the unlocking of the grab jaws by attracting said armsin the opposite direction in opposition to the action of said spring.

4. An electric grab as claimed in claim 3, wherein said arms comprisesmall attraction plates of magnetic material which are placed inoppositely-facing relation to the poles of the electromagnet.

References Cited UNITED STATES PATENTS 3,253,853 5/1966 Loyer et. al.29488 FOREIGN PATENTS 1,329,072 4/1963 France.

10 ANDRES H. NIELSEN, Primary Examiner

